How to ask for her number?

I met someone through a meetup. com volunteer group at a animal shelter. She was very friendly made a lot of eye contact with me and laughed a lot when she talked to me. I meant to get her number before she left but didn't get the chance.

Since we were in this meetup group I have the option of messaging her through that site. I'm contemplating sending a message telling her I thought she was cool and we should get some tea and talk hang some time. It's that or I wait till I see her at another meetup.